1. Field of the Invention
The present invention generally relates to a speed change control system for use in a continuously variable transmission for an automotive vehicle, such as a V-belt type continuously variable transmission, a torodial type continuously variable transmission or the like. More specifically, the present invention relates to an initializing device of the speed change control system for initializing an instruction value for a motor which operates a speed change control value to realize a position of the valve corresponding to a target speed change ration, which initializing is necessary to eliminate an incorrespondence between a rotating position of the motor (i.e. a rotating position of an output element of the motor) and the instruction value for the motor.
2. Description of the Relevant Art
A V-belt type continuously variable transmission will be taken as an example from the continuously variable transmission. A speed change control system of the V-belt type continuously variable transmission, as shown in e.g. the official gazette of Japanese Patent Publication No. 5-78457, calculates a preferably target speed change ratio corresponding to a running condition, to rotate a motor (i.e. to rotate an output element of the motor) such as a step motor, a servo motor or the like based on an instruction value corresponding to the target speed change ration, for operating the speed change control valve so as to realize a stroke position of the valve corresponding to the target speed change ratio. With this operation, the speed change control valve generates a speed change control pressure corresponding to the target speed change ratio to output it. In response to the speed change control pressure, continuous speed changing or speed varying toward the target speed change ratio is carried out in the continuously variable transmission.
By the way, there is a case that the instruction value to the motor becomes incorrespondence with an actual rotating position of the motor. In this case, exact speed change controlling cannot be realized. Accordingly, in the speed change control system for use in the continuously variable transmission, it is conventional to carry out an initialization for making the instruction value to the motor correspond with the actual rotating position of the motor. Thus, there has been proposed, as described in the above-mentioned official gazette, a method of making the motor rotate in one direction at the time when electric power of the device is turned on during stopping of an automotive vehicle mounting the transmission, detecting by a switch that the rotating position of the motor coincides with a reference position to thereby stop the rotation of the motor, and simultaneously with the detection by the switch, initializing the instruction value to the motor to a value corresponding to the reference position.
However, in the above-mentioned known initializing method of the speed change control system, the switch for detecting that the rotating position of the motor coincides with the reference position, is indispensable, so that there are problems that a cost of the system is increased and a possibility cannot be completely eliminated that the initialization is failed due to a breakdown of the switch.
Further, in the known initializing method of the speed change control system, the initialization can be carried out only during stopping of the automotive vehicle in the condition that the electric power is turned on, so that the initialization cannot be carried out so many times. Accordingly, it is difficult to always make the instruction value of the motor correspond with the actual rotating position of the motor.